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Calibrating 1L5

Christopher Hilton-Johnson All Messages By This Member #148545 An oldie, but a goodie! Does anyone have a tried and provenly successful way of getting the linearity and dispersion of the coil adjustments in Calibration section 3 (coils are L191, L192 and L194). of the manual just so - indeed as the pictures show. I am blowed if I can Mine was broken when I got it and had been grievously fiddled with. The coils look and feel delicate (age?) and I am afraid too much tweaking might damage them physically. The manual makes it all sound very simple., but gives no hints of which coil is the dominant one, and what to look for when adjusting the, ir any order of priority. I can either get linearity, but not a full screens worth of pips or I can get a full screen of pips with the right hand side of the trace compressed. I just cannot get both. Incidentally, unless you use the separate sweep input from 549 to 1L5 (as opposed to the internal feed), several of the front panel controls have no effect and this makes calibration very much more difficult. Bit odd that Any hints, tips, notes, howtos etc would all be most useful. thanks in advance
Snappy All Messages By This Member #148552 Did you set the rear sawtooth switch to the right voltage?
Christopher Hilton-Johnson All Messages By This Member #148553 Yup. I can get the necessary 10? time marker pips, but cannot seem to achieve proper linearity across the full width of the trace. As mentioned I get either accuracy and fewer pips or innacuracy and a full load of pips, the right hand half significantly compressed. Uncompressing that part of the trace reduces the number of pips on the left side of the trace. I suppose what I am seeking is either a written howto, or the learning, from someone else, of how to do it in a structured and effective manner. any more thoughts? toggle quoted message Show quoted text On 09/06/2018 04:57, snapdiode via Groups.Io wrote: Did you set the rear sawtooth switch to the right voltage?
Snappy All Messages By This Member #148562 Not very useful thoughts, no. I have a 1L5 as a collection piece. I only briefly looked at the manual. It sounds similar to the 1L20 in that it probably uses the linear sawtooth voltage to sweep a non-linear reactance, ie a varactor. There's probably a waveshaping circuit somewhere in the shape of resistors and diodes to build an exponential curve somehow? I dunno, check all voltages everywhere. Socketed transistors should be removed and reinserted. I'd look at the waveforms on the swept frequency generator, especially that funky one that goes to D164. Check values of resistors around there. This is all speculation.
Harvey White All Messages By This Member #148567 On Sat, 09 Jun 2018 08:30:10 -0700, you wrote: Not very useful thoughts, no. I have a 1L5 as a collection piece. I only briefly looked at the manual. It sounds similar to the 1L20 in that it probably uses the linear sawtooth voltage to sweep a non-linear reactance, ie a varactor. There's probably a waveshaping circuit somewhere in the shape of resistors and diodes to build an exponential curve somehow? I dunno, check all voltages everywhere. Socketed transistors should be removed and reinserted. I'd look at the waveforms on the swept frequency generator, especially that funky one that goes to D164. Check values of resistors around there. I have a little more speculation. Assuming that the control voltage to the varactor is non linear, then the sweep voltage to the horizontal amplifier should be linear, since the varactor voltage is taking care of the non-linearity. That suggests one of two things (or perhaps a combination). One is that the sweep voltage itself is nonlinear. That would certainly give you a compressed trace. The other is that the varactor voltage is not linear, which would compress equally spaced (in frequency) pips. Assuming that the voltage is higher (exponential), then it seems to me that a linear varactor voltage would result in smaller steps, giving you closer "equal frequency" steps. Harvey This is all speculation.
Dave Wise All Messages By This Member #148585 There's no shaping network. The varactor is linearized by a tuned-stub discriminator. FWIW, Dave Wise ________________________________________ From: [email protected] <[email protected]> on behalf of snapdiode via Groups.Io <snapdiode@...> Sent: Saturday, June 09, 2018 8:30 AM To: [email protected] Subject: Re: [TekScopes] Calibrating 1L5 Not very useful thoughts, no. I have a 1L5 as a collection piece. I only briefly looked at the manual. It sounds similar to the 1L20 in that it probably uses the linear sawtooth voltage to sweep a non-linear reactance, ie a varactor. There's probably a waveshaping circuit somewhere in the shape of resistors and diodes to build an exponential curve somehow? I dunno, check all voltages everywhere. Socketed transistors should be removed and reinserted. I'd look at the waveforms on the swept frequency generator, especially that funky one that goes to D164. Check values of resistors around there. This is all speculation.
Christopher Hilton-Johnson All Messages By This Member #148601 Not sure it is as sophisticated as you think! everything done as you suggest, and will look as you also suggest @ D164 waveform. In some way the tail end of the dispersion linearity falls away - will look again at the variactor diode including replacement Speculation is good - it all helps! toggle quoted message Show quoted text On 09/06/2018 16:30, snapdiode via Groups.Io wrote: Not very useful thoughts, no. I have a 1L5 as a collection piece. I only briefly looked at the manual. It sounds similar to the 1L20 in that it probably uses the linear sawtooth voltage to sweep a non-linear reactance, ie a varactor. There's probably a waveshaping circuit somewhere in the shape of resistors and diodes to build an exponential curve somehow? I dunno, check all voltages everywhere. Socketed transistors should be removed and reinserted. I'd look at the waveforms on the swept frequency generator, especially that funky one that goes to D164. Check values of resistors around there. This is all speculation.
Christopher Hilton-Johnson All Messages By This Member #148602 The 549 works perfectly. I have checked linearity of the time matk generator & it is spot on. You may well be correct in that the 50+ year old varactor diode has changed some of its charastics. I think I have a spare, so will replace if necessary. My issue is, from reading the manual, and the brevity of the adjustment instructions to linearise the responses, it ought to be straightforward to achieve calibration, rather than a marathon of unsatisfactory/non linear results1 thanks for joining the thread toggle quoted message Show quoted text On 09/06/2018 17:29, Harvey White wrote: On Sat, 09 Jun 2018 08:30:10 -0700, you wrote: Not very useful thoughts, no. I have a 1L5 as a collection piece. I only briefly looked at the manual. It sounds similar to the 1L20 in that it probably uses the linear sawtooth voltage to sweep a non-linear reactance, ie a varactor. There's probably a waveshaping circuit somewhere in the shape of resistors and diodes to build an exponential curve somehow? I dunno, check all voltages everywhere. Socketed transistors should be removed and reinserted. I'd look at the waveforms on the swept frequency generator, especially that funky one that goes to D164. Check values of resistors around there. I have a little more speculation. Assuming that the control voltage to the varactor is non linear, then the sweep voltage to the horizontal amplifier should be linear, since the varactor voltage is taking care of the non-linearity. That suggests one of two things (or perhaps a combination). One is that the sweep voltage itself is nonlinear. That would certainly give you a compressed trace. The other is that the varactor voltage is not linear, which would compress equally spaced (in frequency) pips. Assuming that the voltage is higher (exponential), then it seems to me that a linear varactor voltage would result in smaller steps, giving you closer "equal frequency" steps. Harvey This is all speculation.
Snappy All Messages By This Member #148608 Yeah I didn't notice that feedback from this discriminator, which in any case I don't understand how it works. The waveform shown in the schematics looks shaped to me. Whatever is doing this shaping deserves investigation. I'd dump the whole circuit into LTSPCE with careful evaluation of paramaters and simulate away! Carbon comp resistors need to be checked for drift. They can go out by 20% or more after so many decades.

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